Heretofore, a data recording medium such as a compact disc (a trade mark) has additional information data (subcode) recorded thereon for realizing random access, in addition to information to be primarily reproduced. The information to be primarily reproduced is subjected to a mechanism for correcting errors with information located before and behind the errors. Specifically, CIRC (Cross Interleaved Reed-Solomon Code) or the like is added to the information for countermeasures to such errors.
Thus, data can be utilized only after the lapse of a time required to read data before and behind certain data for performing the error correction processing and a time required to calculations for the error correction. Essentially, unlike reproducible data, the additional information data is required to be utilized in a shorter time after it is read from a data recording medium, so that the error correction processing is not performed for the additional information data, or different error correction processing with a different calculation method from that for data to be primarily reproduced is employed for the additional information data.
As additional information data for randomly accessing a data recording medium, the most necessary data is information indicative of the position of data on the data recording medium, i.e., the address. Since the compact disc or the like is a data recording medium which was originally created for recording audio data and is characterized in that information is recorded at a fixed bit rate, information (address) for specifying each readout unit (sector) on the data recording medium is represented by a numerical value based on the hour, minute, second and frame, i.e., information (time code) on reproduction passing time from the head of reproduced data.
Due to the characteristic of the compact disc that information is recorded at a fixed bit rate, audio data reproduction passing time information (time code) on the disc increases in proportion to an increase in the distance (address) of data from the head position thereof on the data recording medium, i.e., the disc. Consequently, designation of a particular read-out unit (sector) on the data recording medium may also be realized by specifying the reproduction passing time represented by hour, minute, second and frame.
However, since this address based on hour, minute, second and frame is denoted based on a 60-adic number or a 75-adic number utilizing the number of frames per second, this address cannot be used as it is for a data recording medium used by a computer system which basically specifies addresses with binary codes (which may be denoted in hexadecimal). Thus, the MD (Mini-Disc (a trade mark)) standard and so on employ a binary form as the address for specifying a sector. In this case, although a search cannot be made directly with reproduction passing time information (time code), since information is recorded at a fixed bit rate on the mini-disc and so on, conversion from a binary-form sector address to the reproduction passing time information (time code) can be realized by a proportional calculation.
However, if the bit rate of information varies, the correspondence between the conventional reproduction passing time information represented by hour, minute, second and the number of frames and a sector address cannot be calculated. With a varying bit rate, even if the time code was used as a second address, the rate of increase in the reproduction passing time information (time code) would be different between a higher bit rate portion and a lower bit rate portion, whereby two or more sectors would exist having the same passing time information (time code), or two adjacent sectors would not always have sequential passing time information (time code), causing a problem that the time code is not appropriate as the sector address for specifying a position of data on the data recording medium.
Also, as video data recorded on a data recording medium, video data in conformity to the stipulation of ISO11172-2 (MPEG1 Video) or ISO1818-2 (MPEG2 Video) may be occasionally recorded. This video data suffers from technical restrictions on decoding. Specifically, the decoding cannot be performed from an arbitrary position of a bit stream, but must be always started from an I-picture. In a current video CD or the like, when a search is made on a data recording medium for starting to read data from an arbitrary position, the data read is not always started from head of an the I-picture, so that data cannot be utilized until the next I-picture is reached, causing a problem that the decoding cannot be started for this period.
For reproducing the video data, one may wish to selectively decode only I- and P-picture with a B-picture skipped, or one may wish to selectively decode only I-picture with B- and P-picture skipped. The conventional video CD's and so on, nevertheless, have a problem that they do not contain thereon information indicating at which position of a data recording medium picture data is accommodated and which of I-, P-, and B-picture data is accommodated, or information indicating the head position of such picture data, so that a picture of an arbitrary picture type cannot be selectively reproduced by a search operation.
Furthermore, since respective picture data of the video data, after encoded, are recorded in an order different from the order in which they are displayed, a temporal reference is described in a picture header of the video data for indicating the display order. However, no specific method has been thought for allowing the user to make a search by specifying a number of the temporal reference.
Also, the current data recording medium such as the compact disc has only one bit of management information on copyright, i.e., how to deal with duplication. More specifically, only one bit is assigned to information indicating whether duplication of data recorded on the data recording medium is prohibited or permitted. This limits to only two kinds of determinations, that is, duplication is prohibited or permitted. Thus, such insufficient management information implies a problem that it is impossible to achieve detailed copyright management in combination of a plurality of conditions including whether or not duplication is permitted in a converted analog data form; whether or not duplication is permitted in a digital data form; whether or not data may be output to computer equipment; whether or not data may be output to audio-visual equipment other than a computer; and so on, and that repetitive duplications cannot be restricted.
Also, in the current compact disc and so on, an additional information data portion for use in accessing certain data is provided in a fixed configuration, thus presenting few freedom for using the compact disc in a variety of ways, e.g., for using the compact disc so as to support a plurality of applications.